High pressure pumping system

ABSTRACT

A SYSTEM FOR PUMPING A HYDRAULIC FRACTURING FLUID OR SIMILAR LIQUID CONTAINING SUSPENDED SOLIDS AT HIGH PRESSURE WHEREIN THE SOLIDS-LADEN FLUID IS CHARGED INTO AN ACCUMULATOR AT LOW PRESSURE AND THEN DISPLACED FROM THE ACCUMULATOR AT HIGH PRESSURE WITHOUT PASSING THROUGH THE HIGH PRESSURE PUMPING EQUIPMENT.

2, 1971 J. E. ORTLOFF HIGH PRESSURE PUMPING SYSTEM 4 Sheets-Sheeb 1 Filed Nov. 19; 1968 BLENDER h v P 5 5 a m6 mmmwm ED E FIG. I

JOHN E. ORTLOFF INVEN'IUR.

ATTORNEY F 1971 J. E. ORTLOFF HIGH PRESSURE PUMPING SYSTEM Filed Nov. 19, v1968 4 Sheets-Sheet I W U m M B D N E L H B Q mu w B 5 5 a 4 m V 2 A F O 5% F 5 4 J 4 7 8 a 4 w m EoEwwwm 05d Th ATTORNEY Feb. 2,

J. E. ORTLOFF HIGH PRESSURE PUMPING SYSTEM 4 Sheets-Sheet 3 57 59 j) l LIL L Li 6o 74 FIG. 3 32 35 JOHN E. ORTLOFF l 'llO'V AC 72 l I N VEN TOR.

W E. QA

A T TORNE Y Feb. 2, 1971 J. E. ORTLOFF HIGH PRESSURE PUMPING SYSTEM 4 Sheets-Sheet 4 Filed NOV. 19, 1968 BLENDER FIG. 4

A T TORNEY United States Patent Oflice 3,560,053 Patented Feb. 2, 1971 3,560,053 HIGH PRESSURE PUMPING SYSTEM John E. Ortlolf, Houston, Tex., assignor to Esso Production Research Company, a corporation of Delaware Filed Nov. 19, 1968, Ser. No. 776,949 Int. Cl. B65g 53/30 US. Cl. 302-14 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to the pumping of oilfield hydraulic fracturing fluids and similar liquids contalning suspended propping agents or other solid particles.

(2) Description of the prior art The use of hydraulic fracturing for stimulating the production of crude oil and natural gas from wells penetrating subterranean reservoirs has grown rapidly in recent years. The methods generally employed involve the injection of water, crude oil, or a similar fluid into a well at a rate suflicient to break down the exposed formation and the subsequent introduction of oil, gelled water or other fluid containing suspended sand grains, glass beads, or a similar propping agent into the resultant fracture. The propping agent particles prevent complete closure of the fracture as the fracturing fluid leaks off into the adjacent formation and thus result in permeable channels through which fluids can later be injected or produced. The development of fractures with the required conductivities may in some cases necessitate the pumping of large volumes of fluid containing propping agent particles at pressures of 10,000 lbs. per square inch or higher.

The pumps used in hydraulic fracturing operations are generally high pressure triplex pumps driven by diesel or gas turbine engines. These pumps are usually capable of operating at pressures well in excess of those required in fracturing operations but maintenance costs are generally high because of damage to the liners, valves, and pistons.

Experience has shown that sand grains, glass beads, steel shot, and other materials used as propping agents cause severe wear, particularly where the solid particles are present in high concentrations and high pumping rates are required. It is common practice to install new valves at about eight hour operating intervals and to provide standby units for use in case pump failures occur in the field. This has increased the cost of hydraulic fracturing operations and in some cases has made such operations impractical.

SUMMARY OF THE INVENTION This invention provides an improved system for the high pressure pumping of hydraulic fracturing fluids and similar viscous liquids containing suspended solid particles that alleviate many of the difficulties outlined above. This system involves the suspension of sand or other particulate solids in the fluid by means of a blender or similar equipment, the pumping of the resultant suspension from the blender into the accumulators in each of two or more accumulator banks by means of a low pressure pump, the displacement of solids-laden fluid from each accumulator bank in turn by pumping solids-free fluid from a fluid reservoir into each bank with high pressure pumps, and the displacement of solids-free fluid from each accumulator bank into the fluid reservoir by pumping more solids-laden fluid from the blender into each accumulator bank With the low pressure pump. The apparatus em ployed thus includes a blender, a low pressure pump, a plurality of accumulators, a sufflcient number of high pressure pumps to secure the desired pumping rate, a fluid reservoir, and a control system for operating the equipment to permit continuous pumping of the solids-laden fluid under high pressure. This system avoids the necessity for handling fluid containing the suspended solids with the high pressure pumping equipment and therefore alleviates many of the difficulties due to severe wear of pump valves, liners, and pistons that are normally encountered in pumping fracturing fluid and similar liquids containing suspended solids under high pressures. Equipment maintenance expense and overall pumping costs are often considerably lower than in conventional operations.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 in the drawing is a schematic diagram of equipment useful for the high pressure pumping of fluids containing suspended solids in accordance with the invention; FIG. 2 depicts an alternate arrangement utilizing accumulators connected in series, rather than in parallel as shown in FIG. 1; FIG. 3 is a fragmentary view showing a control system useful with the apparatus of FIGS. 1 and 2; and FIG. 4 depicts another alternate arrangement in which the control system of FIG. 3 may be employed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus depicted in FIG. 1 of the drawing includes a bleander 10 used for the suspension of propping agent particles or other particulate solids in a fluid introduced through line 11 from a tank or other source not shown in the drawing. For hydraulic fracturing and similar operations carried out in the field, this will normally be a conventional track or skid-mounted unit including a tank containing a ribbon mixer and jets for providing the necessary agitation of the fluid and solids. It may also include equipment for monitoring the density of the slurry produced and proportioning devices for the continuous mixing in of both liquid and dry additives. Such units are available in various sizes, depending upon 'the volume of fluid and solids to be handled. A blender with a capacity of about 25 barrels of suspension per minute is adequate for most fracturing operations but larger units may in some cases be used.

One or more propping agent bins or similar devices 12 will normally be used to facilitate rapid addition of the propping agent particles or other solids to the fluid in the blender at a controlled rate. These generally include a belt conveyor or the like for feeding the solids and means for controlling the speed of operation to regulate the feed rate. In many cases, however, it will be satisfactory to load the solids by hand without using an automated loading device.

The blender referred to above is connected to the intake of a low pressure pump 13 by means of line 14, which will ordinarily be a length of hose. The pump employed may be a low pressure centrifugal pump and will often be mounted on the blender itself. Experience has shown that the pumping of fluids containing suspended sand grains or other abrasive particles generally presents few problems at low pressures, even though the solid concentration is quite high, and that centrifugal pumps are therefore generally satisfactory for this purpose. The discharge line 15 from pump 13 is connected to lines 16 and 17 containing check valves 18 and 19 respective y.

The check valves are arranged to permit flow from the pump but prevent the passage of fluid in the opposite direction. Downstream of check valve 18, line 16 is manifolded to the accumulator bank containing parallel accumulators 21, 22, 23, and 24. In like manner, line 17 is manifolded downstream of check valve 19 to a bank containing parallel accumulators 25, 26, 27, 28, and 29. The accumulators will normally be elongated, fully enclosed horizontal tanks provided with inlets at one end and outlets at the other. Each accumulator must be capable of withstanding the maximum pressure developed during the pumping operation. The size of these units will depend primarily upon the particular fluid-solid system to be handled. In general, the unit should be sized so that the residence time in each accumulator is sufliciently short to prevent undue settling out of the suspended particles. If the viscosity of the fluid is low and the difference between the density of the suspended solid particles and that of the fluid is large, the volume of each accumulator will normally be relatively small. If, on the other hand, the fluid has a high viscosity and the density difference is small, each accumulator may be quite large. For field operations, the accumulators will normally be mounted on a truck or trailer to facilitate their transportation.

The outlet lines from each bank of accumulators are manifolded in a manner similar to the inlet lines. Line 30 extends from the manifold connecting accumulators 20 through 24 to a two-way valve 31 and a downstream check valve 32 which prevents flow back toward the accumulators. Line 33 extends in similar fashion from the manifold connecting accumulators through 29 to a two-way valve 34 and a check valve 35. Downstream from the check valves, the two lines feed into line 36 for the discharge of fluid containing suspended solid into a well, a pipeline, or the like.

The fluid used to displace the suspension from the accumulators is stored in a tank or fluid reservoir 37. The volume of this reservoir should be somewhat greater than the volume of the accumulators and connecting lines in the system. A screen 38 is normally installed near the inlet end of the reservoir to isolate any solids that might be entrained in the incoming fluid. Line 39 extends from the reservoir to the inlet side of a plurality of high pressure pumps 40, 41, 42, 43, 44, 45, 46, 47, 48, and 49, connected in parallel. These will normally be high pressure positive displacement pumps. Although ten high pressure pumps are shown in the drawing, a greater or lesser number may be employed. The number used will depend upon the pumping rate required. The discharge lines from the high pressure pumps are manifolded and connected to line 50 which is in turn connected to the intake side of a four-way remotely controlled valve 51. This valve contains one inlet and is designed to permit the discharge of fluid through one of three different outlets. Line 52 extends from one outlet of the four-way valve to fluid reservoir 37 to permit the recycling of solids-free fluid. Lines 53 and 54 containing check valves 55 and 56 extend from other outlets of the valve to lines 16 and 17 at points downstream from check valves 18 and 19. High pressure fluid can thus be injected into either bank of accumulators.

The discharge lines from the two accumulator banks, designated by reference numerals and 33, are connected to the fluid reservoir 37 by means of lines 57 and 58 containing remotely controlled valves 59 and .60 respectively. These latter two valves are provided with screens which surround the valve seats and prevent the entrapment of solid particles between the seats and valve bodies as the valves close. Suitable valves fitted with screens that may be utilized for this purpose are available commercially and will be familiar to those skilled in the art.

FIG. 2 of the drawing illustrates an alternate arrangement of the apparatus in which the accumulators 20 through 24 and 25 through 29 are connected in series instead of in parallel. The components used are the same in both arrangements and hence the same reference numerals are used to identify individual pieces of equipment. This use of the accumulators in series is advantageous in certain cases because it eliminates the possibility of by-passing individual accumulators when displacing the fluid containing suspended solids from an accumulator bank.

A control circuit that may be utilized with either the system of FIG. 1 or that of FIG. 2 is depicted in FIG. 3 of the drawing. The circuitry employed included pressure sensitive electrical switches 70 and 71 located in lines 53 and 54 respectively at points downstream from check valves 55 and 56. Switch 70 controls the current flowing in parallel loops extending from a volt alternating current source 72 through the coil of a solenoid 73 associated with remote control valve 59 and a solenoid 74 associated with remote control valve 60. These solenoids are arranged so that valve 59 is opened and valve 60 is closed when switch 70 is closed and the circuits are energized. Pressure sensitive switch 71 controls the current in parallel loops extending through solenoids 75 and 76, associated with the same two remote control valves. When switch 71 is closed and the associated circuits are energized, valve 59 is closed and valve 60 is opened. This permits cyclic operation of the system so that fluid containing suspended solids from one bank of accumulators is passed to the well, pipeline, or the like through line 36 while fluid free of solids from the other bank of accumulators is being returned to the fluid reservoir 37. Switches 70 and 71 are actuated alternately in response to changes in pressure produced by the movement of four-way valve 51. This valve permits high pressure fluid to pass from line 50 through either line 53 or line 54 but not through both simultaneously. Only one pressure-sensitive switch is therefore closed at any one time. The four-Way valve may be operated manually if desired but will normally be motor-driven and provided with a timer so that fluid flow is switched from line 53 to line 54 and back again at predetermined intervals. It will be understood, of course, that the invention is not restricted to this particular control system and that other systems can also be employed.

The apparatus described above is used for the pumping of liquid containing suspended solids by first starting the blender 10. Oil, water, or other liquid is introduced into the blender through line 11. The propping agent particles or other solids to be suspended in the liquid are added from bins 12. After the blender is operating satisfactorily, the liquid-solid suspension formed therein is withdrawn through line 14 to low pressure pump 13 and pumped through lines 16 and 17 into the two accumulator banks. During this initial stage of the operation, the automatic control system is not actuated. The two-way valves 31 and 34 are kept closed to prevent any fluid from passing through line 36 to the well, pipeline or conduit through which the suspension is to be pumped. The remotely con trolled valves 59 and 60 are operated manually so that both are in the open position. Any air, gas or liquid present in the accumulators on startup can thus be displaced by the incoming slurry through lines 57 and 58 to the fluid reservoir 37. Check valves 18 and 19 permit the.

passage of the suspension to the accumulators and check valves 55 and 56 prevent the suspension from passing through lines 53 and 54 to the four-way valve 51.

After the accumulators 20 through 24 and 25 through 29 have been filled, the low pressure pump 13 and the blender 10 are temporarily shut down. The manually operated two-way valves 31 and 34 are opened. Four-way valve 51 is positioned so that fluid can be pumped through line 50 into line 53 and to accumulators 20 through 24. Remotely controlled valves 59 and 60 are operated manually so that valve 59 is open and valve 60 is closed.

Once the valves have been set, the high pressure pumps 40 through 49 are started. Fluid from reservoir 37 is withdrawn through line 39 to the pump manifold and pumped through lines 50- and 53 to accumulators 20 through 24. The suspension initially present in these accumulators is displaced by the incoming fluid through lines 30 and 36 to the well, pipeline, or other conduit. Check valves 18 and 35 prevent flow of the solids-free liquid and suspension into other parts of the system. Pumping is continued under high pressure until sufficient solids-free liquid from reservoir 37 has been injected into accumulators 20 through 24 to displace the suspension initially present therein. At this point, accumulators 20 through 24 will contain solids-free liquid and accumulators 25 through 29 are filled with liquid containing suspended solids.

The automatic control system shown in FIG. 3 of the drawing is now actuated. Four-way valve 51 is repositioned so that fluid from the high pressure pumps passes through line 54 to accumulators 25 through 29. Pressure sensitive switch 70 in the control system energizes solenoids 73 and 74 so that remote control valve 59 is in the open position and valve 60* is closed. Low pressure pump 13 and blender are started so that fluid containing suspended solids is pumped through line 16 and check valve 18 into accumulators 20 through 24. The high pressure downstream of check valve 19 keeps this valve closed. The fluid and suspended solids injected into accumulators 20 through 24 displace solids-free liquid through line 57 into fluid reservoir 37. Simultaneously, fluid containing suspended solids initially present in accumulators 25 through 29 is displaced at high pressure by solids-free fluid through line 33 and check valve 35 to line 36 leading to the well, pipeline or other conduit. The high pressure closes check valve 32 and prevents flow of the fluid and suspended solids to other parts of the system. The pumping of the fluid containing suspended solids into accumulators 20 through 24 at low pressure and solids-free fluid into accumulators 25 through 29 at high pressure continues until the fluid initially present in both accumulator banks has been displaced. When this point is reached, four-way valve 51 is changed to divert the solidsfree fluid through line 53 into accumulators 20 through 24. This closes check valve 18 and permits check valve 19 to open. Remotely controlled valve 60 is simultaneously opened and valve '59 is closed by the activation of pressure switch 71. The fluid containing suspended solids from accumulators 20 through 24 is now discharged at high pressure through line 30, check valve 32 and line 36 to the well, pipeline, or other conduit while solids-free fluid from accumulators 25 through 29 is being returned to tank 37. The high pressure closes check valve 35 to restrict the flow to line 36. The operation is continued in this cyclic fashion until the desired volume of fluids containing suspended solids has been delivered to the well, pipeline or other conduit.

FIG. 4 in the drawing illustrates a further embodiment of the invention in which balls or pigs are used to separate solids-laden fluid from solids-free fluid in the accumulators. The apparatus of FIG. 4 is generally similar to that of FIGS. 1 and 2 but utilizes two elongated accumulators 80 and 81 in place of the accumulator banks described earlier. Components which are common to the embodiments of FIGS. 1 and 2 and that of FIG. 4 are identified by the same reference numerals. The two accumulators 80 and 81 are of substantially uniform diameter over their entire length and are fitted with pig launchers 82 and 83 near their upper ends. These launchers include solenoid operated gates 84 and 85 by means of which balls or pigs 86 are released one at a time into the accumulators. The pig launchers can be controlled by means of timers similar to that used to control the operation of four-way valve 51 or can be actuated in response to changes in pressure in the system by electrically connecting the solenoid coils into the circuits containing pressure switches 70 and 71 in FIG. 3.

Each of the accumulators of FIG. 4 is also fitted with a pig trap near its lower end. These traps, identified by reference numerals 87 and 88, include solenoid operated gates 89 and 90. Gates 84 and 89 operate simultaneously, as do gates and 90. Here again timers or the pressure switches referred to above can be utilized to control the frequency of operation. The electrical connections for actuating the gates with the pressure switches will be obvious to those skilled in the art.

The operation of the apparatus of FIG. 4 is similar to that of the earlier embodiments except that the pig launcher and pig trap gates are actuated each time an accumulator is switched from solids-free to solids-laden fluid or vice versa. This results in the insertion of a ball or pig between adjacent batches of solids-free and solidsladen fluid and reduces adverse effects due to mixing. The balls or pigs must be transferred from the traps to the launchers periodically and hence it will generally be preferable to employ traps and launchers capable of holding more than the four balls or pigs shown. This and similar modifications to the apparatus depicted will be apparent to those skilled in the art.

It will be apparent from the above description of the system that the method and apparatus of the invention permit the pumping of fluids containing suspended solids at high pressures without the necessity for passing the solids through the high pressure pumping equipment. This alleviates difiiculties normally encountered due to wear of the high pressure pump valves, liners and pistons and often permits substantial reductions in over-all pumping costs. Although the system has been described primarily in terms of hydraulic fracturing operations, it will be apparent that the method and apparatus can in some cases be employed for abrasion drilling and other operations that also require the pumping of liquids containing suspended solids under high pressures.

What is claimed:

1. A system for pumping a fluid and suspended solids which comprises: a blender for suspending solid particles in an input liquid; a low pressure pump; a low pressure intake line extending from said blender to said low pressure pump; a first accumulator; a second accumulator; a low pressure discharge line extending from said low pressure pump to each of said accumulators, said discharge line containing check valves for preventing backflow from each accumulator; a fluid reservoir; a low pressure recycle line extending to said reservoir from each of said accumulators, said recycle line containing remotely-controlled valves for controlling the recycle of fluid form each of said accumulators; a high pressure pump; a high pressure intake line extending from said fluid reservoir to said high pressure pump; a high pres sure discharge line extending from said high pressure pump to each of said accumulators, said discharge line containing a valve for alternately directing fluid to one of said accumulators and then the other and check valves for preventing backflow from each accumulator; means responsive to pressure downstream of said check valves in said high pressure discharge line for actuating said remotely-controlled valves in said recycle line to permit the alternate recycling of fluid from one of said accumulators and then the other; and discharge lines extending from each of said accumulators for the discharge of fluid containing suspended solids, said discharge lines containing check valves for preventing backflow to each accumulator.

2. Apparatus as defined by claim 1 wherein said first and second accumulators are fitted with pig launchers and pig traps.

3. Apparatus as defined by claim 1 wherein said first accumulator is one of a first plurality of accumulators connected in parallel and said second accumulator is one of a second plurality of accumulators connected in parallel.

7 8 4. Apparatus as defined by claim 1 wherein said first 3,254,924 6/1966 Harrison et al 30 2-14 accumulator is one of a first plurality of accumulators 3,312,506 4/1967 Baker 30266 connected in series and said second accumulator is one 3,328,089 6/1967 Hodgson et a1. 30214 of a second plurality of accumulators connected in series. 3,449,013 6/ 1969 Sakamoto et a1 30 2-14 References Cited 5 EVON C. BLUNK, Primary Examiner UNITED STATES PATENTS R. S. GAITHER, Assistant Examiner 2,672,370 3/1954 Jones et a1. 302-14 2,708,140 5/1955 Reed 302 44 3,140,123 7/1964 Bowen 302 14 0 30266 

